The invention relates to a method for measuring the diameter of an elongated article, in particular a cable of a small diameter, according to the preamble of patent claim 1.
It is known to determine the diameter of cables or other elongated articles in an optical way in that it is irradiated with the light of a light source, wherein the main beam direction is approximately perpendicular to the longitudinal axis of the article. On the opposite side the light under the application of refracting surfaces (lenses, objectives, etc.) is projected onto a cellular light-sensitive sensor, wherein the measured object casts a shadow onto the line sensor. The shadow edges are acquired; their distance is a measure of the diameter.
With the practical application of the known device it is hindered by contaminations at the light entrance openings and light exit openings. It is therefore also known to so select the optic that at the light entrance and light exit openings the light becomes defocussed. Partial contaminations influence the measurement then only in a limited manner.
The known optical devices function in principle in a satisfactory manner, but are however relatively complicated and have a large construction.